(1) Field of the Invention
The present invention relates to a method of supporting a wafer, a wafer supporting apparatus and a wafer mounter having the apparatus, which are used when a plastic tape is applied to the wafer.
(2) Prior Art
A number of semiconductor elements are sheared from a wafer in length and breadth. When the semiconductor elements are divided from the wafer, a plastic tape is applied to the reverse side of the wafer prior to division of the wafer in order to prevent the divided semiconductor elements from separating unnecessarily. The taping operation is carried out automatically by utilizing a so called table mounter.
Normally, the table mounter is constructed as follows. A wafer take-in device takes in wafers one by one from a wafer stock jig and after regulating a direction of the wafer by means of a wafer direction determining device, the wafer is transfer device in such a state that the wafer is rotated. On the other hand, an outer frame direction determining device takes in an outer frame one by one from an outer frame stock jig and regulates a direction of the outer frame and thereafter the outer frame is transferred to the tape applying stage by means of an outer frame transfer device. Thereafter, a tape applying device presses and applies a tape to the wafer which is supported by a wafer supporting device on the tape applying stage, and also to the outer frame which is supported by the outer frame supporting device on the tape applying stage. Then, unnecessary portions of the tape applied to the wafer and the outer frame are cut and removed by a cutting device, and the wafer, the outer frame and the tape, which are adhered to one another, are transferred by a conveying device from the tape applying stage into a predetermined jig such as the outer frame stock jig.
Transfer of the wafer and transfer of the outer frame to the tape applying stage may be carried out at the same time in order to shorten a cycle time. Further, the transfer may be carried out sequentially step by step in order to prevent crossing operations of the wafer transfer device and the outer frame transfer device.
For example, as shown in FIG. 8, a wafer supporting device 100 as mentioned above comprises a table plate 101, a receiver 102 in the shape of substantially a ring which projects from the upper surface of the table plate 101 to correspond to a peripheral edge of a wafer W, a vacuum opening 103 formed with the upper surface of the receiver 102 and connected to a vacuum source, a pressure space 104 formed between the table plate 101 and the wafer W which is set reversely on the receiver 102, and a compressed air supplying opening 105 formed with the upper surface of the table plate 101 and inside the receiver 102 and connected to a compressed air supplying source.
The peripheral portion of the wafer W is sucked to the receiver 102 immediately after the wafer is set reversely on the receiver 102 and immediately before removing it. When a tape applying device applies a tape to the wafer, a compressed air, the pressure of which is controlled by a micro-regulator, is supplied from the compressed air supplying source in order to support the wafer W.
In the prior art, where the supporting pressure acting on the wafer W from the pressure space 104 is set greater than the sucking pressure acting on the receiver 102 for sucking the peripheral portion of the wafer W, it becomes unstable to secure the wafer W onto the receiver 102, and as the result it is in danger of displacement of the wafer W. Therefore, the supporting pressure acting on the wafer W cannot be set greater than the sucking pressure for sucking the peripheral portion of the wafer W onto the receiver 102.
Further, the sucking force acting on the peripheral portion of the wafer W corresponds to an opening area of the sucking opening 103, but the opening area of the sucking opening 103 substantially corresponds to a size of the wafer W. Therefore, the sucking force acting on the peripheral portion of the wafer W is limited corresponding to a size of the wafer W and this means that the supporting pressure acting on the wafer W is also limited corresponding to a size of the wafer W. Further, a size of the opening area of the sucking opening 103 is in proportion to a diameter of the wafer W where the opening width of the sucking opening in a radial direction thereof is the same regardless of the size of the area of the sucking opening. On the other hand, the area of the pressure space 104 contacting the wafer W is in proportion to a diameter of the wafer W by self-multiplication and therefore the supporting pressure per area for the wafer becomes smaller as the diameter of the wafer becomes larger. As a the result, when the diameter of the wafer becomes large, the supporting pressure becomes insufficient so that the wafer W cannot be sufficiently pressed to the tape and bubbles may sometimes occur between the wafer W and the tape.
Particularly, according to the above conventional art, the tape cannot be applied to the wafer W having a diameter of 8 inches without occurring bubbles between the wafer W and the tape, and bubbles may sometimes occur in applying the tape to the wafer W having a diameter of 5 inches.
Where the bubble occurs between the wafer W and the tape, a problem may occur such that the semiconductor elements are blown out due to popping of the bubbles at the time of division into pieces, and that the semiconductor elements supported by the tape may be damaged by the semiconductor elements which are blown out.